This invention relates to a method and apparatus for adjusting the voltage of railroad incandescent signal lamps, and, in particular, to the measurement of voltages and currents at the power source for a lamp circuit to determine the voltage setting necessary to produce a desired voltage at an incandescent lamp remote therefrom without having to measure the voltage at the lamp.
Historically, a battery has been used to drive railroad signal lamps. Typically the battery voltage is not well defined and can vary for example due to temperature changes, battery charger characteristics, loss of power, or system load variations. Because high line voltages decrease lamp life, the voltage at the lamp is commonly set lower than the rated voltage for that lamp. For example, the voltage for a ten-volt lamp will be set to nine volts to avoid a high line voltage that could burn out the bulb.
Railroad lamp voltage adjustment has been a two-person operation with one person measuring the voltage at the signal lamp and calling to a second person at the control system who adjusts a series resistor or adjustable regulator at the voltage feed point until the desired voltage is measured at the lamp. The signal lamp control system is typically fifty to two hundred fifty feet away from the signal lamps. Additionally, the length of the power cable to the signal lamps can vary widely from location to location.
Lamp bulb life can be extended if the lamp power source voltage is adjusted to an optimum operating point. At each signal location the wiring differs, in some cases substantially enough that individual lamp adjustment has become a common, and time consuming, ritual to extend signal lamp life. Lamp bulbs are regularly replaced every six months to avoid the problem and expense of a lamp burning out during operation. Additionally, because the electrical characteristics of lamps can vary by as much as twenty percent, each time a bulb is replaced the voltage has to be readjusted. Likewise, any component of the control system is replaced, the power supply voltage has to be readjusted.
It is, therefore, the primary objective of the present invention to provide a method and apparatus for determining the output voltage of a power source necessary to produce a desired lamp voltage at an incandescent lamp using voltage and current measurements at the power source.
Another important objective of the present invention is to provide a method and apparatus that eliminates the need to measure voltages at an incandescent lamp remote from the power source.
Yet another important objective of the present invention is to provide such a method and apparatus that saves time and labor cost by eliminating the need for a second person to travel to the site and measure voltages at an incandescent lamp remote from the power source.
Still another important objective of the present invention is to provide a method and apparatus that extends the life expectancy of incandescent lamps by improved control of the lamp voltage using measurements at the power source to adjust for circuit resistance.
Yet another important objective of the present invention is to provide a method and apparatus that controls and stabilizes the intensity of incandescent lamps by improved control of the lamp voltage using measurements at the power source to adjust for circuit resistance.
These and other objects of the invention are achieved by a microprocessor based system that automatically determines the voltage output required at a power source to produce a desired lamp voltage without having to directly measure the voltage at the lamp. This is accomplished by automatically measuring the voltage across a circuit that includes a 40-ohm resistor in series with a lamp output switch and a signal lamp, and measuring the current therein with the lamp dark. This is referred to as a xe2x80x9ccoldxe2x80x9d test because the resistance of the dark lamp filament is a factor in the voltage and current measurements. The resistor is then removed from the circuit and the voltage and current for the operational circuit is measured while the filament is illuminated. This is referred to as a xe2x80x9chotxe2x80x9d test because the resistance of an illuminated lamp filament is a factor in the voltage and current measurements.
A first wiring resistance, excluding the lamp filament resistance, and a more accurate second circuit resistance are calculated based on the voltage and current measurements and empirically determined constants relating to railroad signal lamps. From these calculations the power source voltage setting is determined and set without the need to directly measure the circuit resistance or the voltage at the lamp.